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Objectives for today: describe how heart action is coordinated with

reference to the sinoatrial node (SAN), theatrioventricular node (AVN) and the Purkyne tissue.

interpret and explain electrocardiogram (ECG) traces,with reference to normal and abnormal heart activity.

Syllabus: 1.2.2 g & h Homework: continue revising for your January exam!Now: match up the questions and answers on thedominoes. They should go in a big loop.

http://www.youtube.com/watch?v=AAe3cabBLaM http://www.nhlbi.nih.gov/health/dci/animate/electrical.swf

http://www.youtube.com/watch?v=AAe3cabBLaMhttp://www.nhlbi.nih.gov/health/dci/animate/electrical.swfhttp://www.nhlbi.nih.gov/health/dci/animate/electrical.swfhttp://www.youtube.com/watch?v=AAe3cabBLaM

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Purkyne fibres: British poor -kin- yuh

Purkinje fibres: American poor -kin- jee

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Control of heartbeat 1. The heart beat is initiated by the SAN (the pacemaker). It

initiates a wave of depolarisation : also often called a

wave of excitation . This is a change in the distribution of charges on either side of cell membranes like a nervousimpulse.

2. The wave of depolarisation spreads over the 2 atria,

causing them to contract.3. The wave of depolarisation reaches the AVN , but is delayedbefore being relayed down the bundle of His and thePurkyne tissue . This delay ensures that the ventricles

contract after the atria.4. This wave of depolarisation then spreads through the wallsof the ventricles... making them contract upwards, awayfrom the apex (the pointy bit at the bottom of the heart).

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The ECG displays voltage changes against time.

Time (s)

V o

l t a g e ( m

V )

ECGs show the changes in charge distribution in the heart tissue. Depolarisation (the charge differences decrease) causes contraction. Repolarisation (the charge differences are re-established) causes

relaxation.

Patients with heart problems will have a different ECG trace.

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And now:

1.Read p.70-72 in the green books and p.58-59 in thepurple books.

2.Annotate your ECG trace to say what is happening ateach point.

3. Do the Diagnosing heart problems from ECG tracessheet.

Extension:

1.Try SAQ6 on p.71 of the green books. Answers onp.246.

2.Try Qs 1, 2, 3 & 5 (not Q4) on p.59 of the purplebooks. Answers on p.238.

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8 - R

2 - S

3 - Y

4 T

6 - U

1 Z

5 - X 7 V